Nonvolatile memories are semiconductor memories that retain their contents even when unpowered. Flash memory is a type of nonvolatile memory that can be electronically erased and programmed. A flash memory device stores data on a charge storage layer (also known as a floating gate), which can be programmed and erased using an adjacent control gate.
The control gate is separated from the charge storage layer by an insulating layer known as a charge blocking layer. The charge blocking layer prevents charge from leaking off of the charge storage layer and into the control gate, adjacent cells, or contact lines, thereby improving memory retention. The charge blocking layer may be a high dielectric constant (high-K) layer, for example.
Various material systems have been used for charge blocking layers. One of the most common materials is a composite layer including a layer of silicon nitride (Si3N4) surrounded by two layers of silicon dioxide (SiO2). This composite is also known as an oxide-nitride-oxide, or ONO layer. ONO layers provide good charge blocking characteristics, but may not have a sufficiently high dielectric constant or other characteristics necessary for smaller size (e.g. ˜40 nm or less) memories.
Thus, what is needed is a charge blocking layer that is tailorable to smaller memories.